As a conventional rotary machine control apparatus, JP 2010-252432A, for example, proposes model estimation control for operating an inverter. In this control, currents of a three-phase motor are estimated in correspondence to various operation states of the inverter and differences between the estimated currents and command currents are minimized. According to this control, since the inverter is operated to optimize a change of the current estimated based on the operation state of the inverter, it is possible to control the currents to properly follow the command value at transient operation time. The model estimation control is thus considered to be useful for a motor/generator control apparatus or the like in a vehicle, in which particularly high performance is required as a transient follow-up characteristic.
For estimating a current, a sensor is necessary to detect an initial current value. In case of a three-phase motor, two or more sensors are generally needed to detect at least currents flowing in two phases. This adds costs.